1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, an apparatus for cutting a substrate and method thereof. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for cutting a liquid crystal display mother substrate.
2. Discussion of the Related Art
Since the information communication field is developing rapidly, display devices for disposing and displaying information are actively being developed. A cathode ray tube (CRT) has been popular as an information display due to its excellent screen brightness and capability of displaying various colors. However, as the demand for wide-screen, portability and high resolution rises, many recent efforts have been made to research and develop flat panel displays to replace the heavy and large CRT.
Flat panel displays, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescent display (ELD) devices and vacuum fluorescent display (VFD) devices have been the focus of recent research because of their excellent characteristics of light weight and low power consumption. These flat panel displays have wide applications in computers, airplanes, spaceships and the like. In addition, a plurality of unit flat panel display devices can be fabricated in one manufacturing process by forming semiconductor chips of a large scale integrated circuit and the like in a matrix form on a brittle substrate and cutting the substrate into device units.
In cutting a brittle substrate of glass, silicon, ceramic or the like, there are a dicing method using a 50˜200 μm thick diamond blade, which is rotating at a high speed, to form a cutting groove on the substrate, and a scribing method using a diamond scribing wheel of 0.6˜2 mm thick to form a cutting groove on a surface of the substrate. In the dicing method, because the blade is considerably thinner than the scribing wheel, the dicing method is suitable for cutting a substrate having thin film or prominences on its surface.
However, since a frictional heat is generated at a zone that is being cut by the blade, the blade cutting is carried out by supplying a coolant or cooling water to the corresponding zone and it is difficult to completely remove the coolant after completion of dicing. Thus, if moisture remains due to the incomplete removal of the cooling water, it is highly probable that any metal parts will corrode. Thus, the dicing method is not suitable for a flat panel display including metal parts, such as a metal electrode layer, a metal terminal and the like. In addition, a cutting time of the dicing method is longer than that of the scribing method, thereby lowering productivity. In contrast, the scribing method does not require coolant or cooling water to enhance throughput of product, and the cutting time of the scribing method is shorter than that of the dicing method, thereby increasing productivity.
FIG. 1 is a flowchart of a general process for fabricating a liquid crystal display panel. In FIG. 1, at step S1, a thin film transistor (TFT) array substrate having a plurality of transistors and a color filter substrate including a color filter are separately prepared. For example, the TFT array substrate is prepared by depositing and patterning a plurality of layers, including pixel electrodes, on a first substrate. Because the number of masks are used in patterning the layers, many efforts have been made to lower the number of masks to reduce fabrication cost. The color filter substrate is prepared by sequentially forming an R/G/B color filter and a common electrode. The color filter is formed by dyeing, printing, pigment dispersion or electrophoretic deposition. The pigment dispersion is widely used for forming the color filter.
Subsequently, at step S2, alignment layers are respectively formed on the TFT array substrate and the color filter substrate. The alignment layers are formed by coating a polymer film and rubbing the polymer film. The polymer film is commonly formed of a polyimide-based organic substance, and the rubbing process is used to align the alignment layer. The rubbing process, which includes the step of rubbing the alignment layer in a predetermined direction using a rubbing cloth, is suitable for mass production and is advantageous in facilitating a control of the pretilt angle with stable alignment. Recently, a photo alignment method using a polarized light is developed and used.
At step S3, a seal pattern is formed on one of the TFT array substrate and the color filter substrate. The seal pattern is located at a periphery of a display area and includes a gap for liquid crystal injection. The seal pattern also prevents leakage of the injected liquid crystal molecules. The seal pattern is formed by forming a thermo-hardening resin with a predetermined pattern using a screen print method or a seal dispenser method.
At step S4, spacers uniform in size are scattered on one of the TFT array substrate and the color filter substrate to maintain a uniform and fine gap between the TFT array substrate and the color filter substrate. The spacers are scattered by wet scattering with a mixture of spacers and alcohol and the like or dry scattering by spraying spacers only. Dry scattering is divided into electrostatic scattering using static electricity and non-electric scattering using a gas pressure. Since the liquid crystal display device is vulnerable to static electricity, non-electric scattering is widely used.
At step S5, the TFT array substrate and the color filter substrate are loaded in a bonding chamber and are bonded to each other by pressurizing and hardening the seal pattern. As a result, the TFT array substrate and the color filter substrate are arranged with the alignment layers on the TFT array and color filter substrates facing each other and the pixel electrode facing the color filter in one-to-one manner.
At step S6, the bonded substrates are cut into a plurality of unit LCD (liquid crystal display) panels. In general, a plurality of unit LCD panels, each of which corresponds to one LCD, are formed on one substrate that will be separated into a plurality of the LCD panels to enhance fabricating efficiency and to reduce manufacturing costs. In the LCD panel cutting process, the scribing method is used. In particular, a scribe line is formed on a surface of a substrate using a scribing wheel of diamond having hardness higher than that of a glass substrate or a laser application to generate a crack in a substrate thickness direction.
At step S7, liquid crystal molecules are injected between the alignment layers of the bonded substrates to form a liquid crystal layer. The liquid crystal injection is carried out by vacuum injection using a difference between inner and outer pressures of the LCD panel. When the liquid crystal molecules are injected in the LCD panel, air amongst the liquid crystal molecules creates bubbles within the LCD panel that cause device failure. To prevent the bubble generation, a process of removing the bubbles by leaving the liquid crystal molecules in a vacuum state for a considerable time is needed. After completion of the liquid crystal injection, the inlet is sealed to prevent the liquid crystals from flowing out via the inlet. In this case, the inlet is blocked in a manner of coating a UV-hardening resin on the inlet using a dispenser and hardening the coated resin by UV-ray application.
At step S8, polarizing plates are respectively attached to each outer surface of the above-prepared LCD panel and a driving circuit is connected to the LCD panel to complete the liquid crystal display device.
A substrate cutting method and apparatus according to a related art are explained with reference to the attached drawings as follows.
FIGS. 2A to 2F are diagrams illustrating a sequence of cutting a mother substrate into unit LCD panels according to the related art. FIGS. 2A to 2F illustrate six LCD panels (e.g., 18.1″ each) arranged on a mother substrate (e.g., 1,000 mm×1,200 mm). Referring to FIG. 2A, a bonded mother substrate 52 is loaded on a table 51 of a loader. The bonded mother substrate 52 includes a TFT substrate 52a and a C/F (color filter) substrate 52b. In FIG. 2A, an upper figure indicates a cross-sectional diagram of the mother substrate 52 loaded on the table 51, and a lower figure indicates a layout of the mother substrate 52 loaded on the table 51.
Referring to FIG. 2B, the mother substrate 52 is inversed such that the TFT substrate 52a is placed on a topside. Subsequently, a diamond based wheel 53 having hardness higher than a glass substrate is aligned on a cutting-reserved line of the TFT substrate 52a. The wheel 53 is then rotated and moved to form a crack having a predetermined depth in a direction of a long or short axis (shown as arrows) of the TFT substrate 52a. 
Referring to FIG. 2C, the mother substrate 52 is inversed again such that the C/F substrate 52b is placed on a topside. A break bar 54 is then aligned on the C/F substrate 52b. By pressurizing the break bar 54, the crack formed having the predetermined depth on the TFT substrate 52a is fully cut to separate the TFT substrate 52a into unit LCD panels.
Referring to FIG. 2D, the wheel 53 is aligned on a cutting-reserved line of the C/F substrate 52b. The wheel 53 is then rotated and moved to form a scratch having a predetermined depth in a direction of a long or short axis (shown as arrows) of the C/F substrate 52b. 
Referring to FIG. 2E, the mother substrate 52 is inversed again such that the TFT substrate 52a is placed on a topside. The break bar 54 is then aligned on the TFT substrate 52a. By pressurizing the break bar 54, the crack formed having the predetermined depth on the C/F substrate 52b is fully cut to separate the C/F substrate 52b into unit LCD panels. After completion of the LCD panel separation, an unnecessary dummy substrate is removed.
Referring to FIG. 2F, the substrates of the unit LCD panels are unloaded once using a suction plate (not shown in the drawing) to be carried and prepared for the next process.
FIG. 3A is a cross-sectional diagram illustrating a substrate cutting apparatus according to the related art, and FIG. 3B is a plane view illustrating the substrate cutting apparatus shown in FIG. 3A. In FIG. 3A and FIG. 3B, a substrate cutting apparatus includes first and second belt conveyers 70 and 80 arranged with a predetermined distance spaced apart from each other to load and convey a mother substrate 60 to be cut. The substrate cutting apparatus also includes servo motors 90 provided at ends of the first and second belt conveyers 70 and 80 to drive the first and second belt conveyers 70 and 80, respectively, and a scriber 100 provided between the first and second belt conveyers 70 and 80 to perform a scribing along a cutting-reserved line on the substrate 60.
The first belt conveyer 70 includes a plurality of conveyer support beams 71 arranged in a Y-axis direction to be evenly spaced apart from each other and a plurality of beam support bar frames 72 arranged in an X-axis direction to support the conveyer support beams 71. Similarly, the second belt conveyer 80 includes a plurality of conveyer support beams 81 arranged in the Y-axis direction to be evenly spaced apart from each other and a plurality of beam support bar frames 82 arranged in the X-axis direction to support the conveyer support beams 81. In addition, the scriber 100 includes a scribe head 101, a guide bar 102 having the scribe head 101 attached thereto, a pair of support bars 103 respectively supporting both sides of the guide bar 102, and a pair of guide rails 104 arranged in parallel to secure the support bars 103.
A substrate cutting method using the above-configured related art substrate cutting apparatus is explained as follows. First, the substrate 60 loaded on the first belt conveyer 70 is moved in one direction as the first belt conveyer 70 is driven by the servo motor 90. Subsequently, if a cutting-reserved line of the moved substrate 60 is placed between the first and second belt conveyers 70 and 80 (one end of the substrate 60 is placed on the first belt conveyer 70 and the other end of the substrate 60 is placed on the second belt conveyer 80), the scribe head 101 is actuated to move in a direction perpendicular to the moving direction of the substrate 60 to perform a scribing process along the cutting-reserved line of the substrate 60.
After the scribed substrate 60 is completely conveyed to the second belt conveyer 80 from the first belt conveyer 70, a new substrate is loaded on the apparatus to perform the scribing process on the newly loaded substrate. Subsequently, the scribed substrate is separated into unit LCD panels via a break process.
The related art substrate cutting apparatus and method have the following problems. First, vibration is generated from the scribing process or the guide rails. In particular, since the support beams and the belt conveyers have elasticity higher than that of other supports, the vibration is transferred thereto. Subsequently, the generated vibration is transferred to the substrate such that the substrate is separated in the middle of the scribing process. Hence, it is unable to carry out the scribing process on a next substrate smoothly.
In addition, in the X-axis scribe of the related art, the scribe damage is not formed to the uniform depth due to the belt interval and shaking by the conveyer support beam arranged in the Y-axis direction. Such a damage depth is further varied due to unevenness of the belt conveyer. Thus, a portion having the high damage depth may be separated in the middle of the scribing process. Further, the conveyer support beam and the beam support bar frame are deformed due to the vibration that twists the conveyer leveling.